Study On Interface Polarization Of Detection Electrode Of Electrical Tunneling Method

With the rapid development of China's transport industry,a large number of tunnel works need to be built such as highways,railways.TBM(Full cross-section tunnel boring machine)is more and more widely used in tunnel engineering in China because of its fast excavation speed,small disturbance of surrounding rock,good construction quality and high degree of mechanization.During TBM tunnel construction process,fault crushing zone,landslide,gas and cave rock burst and other adverse geological conditions,will inevitably appear causing great damage.It is necessary to timely detect the unfavorable geological body in front of the tunnel,take appropriate measures to avoid or reduce the occurrence of disaster to ensure construction progress safe and successful.BEAM(Bore-tunneling electrical ahead monitoring)is an on-line advanced geological exploration method developed specifically for TBM tunneling.However,during the BEAM prospecting,the cutter head metal serves as the supply electrode as well as the measuring electrode.Therefore there is an interface polarization between the cutter head metal and the geological body,which covers the true polarization of the geological body,resulting in inaccurate detection of polarization caused by unfavorable geological body.The interface polarization voltage between the metal electrode and the rock mass must be deducted in order to improve the sensitivity of BEAM prospecting.In this paper,an extrapolation method was proposed and a detection system was established to measure the interface polarization voltage.The effects of frequency,measurement electrode,supply electrode,current density and water content on the interface polarization were discussed.Results show that this method can successfully measure the interfacial voltage between electrode and geological body.In the frequency range of 0.1 ~ 100 Hz,induced polarization is slightly affected by influencing factors and has a good experimental reproducibility.The use of different measuring electrodes has no effect on medium polarization and interface polarization.Using different power supply electrodes,interface polarization voltage varies,while volume polarization remains the same.The order of interfacial voltage is: 2A12 aluminum>H62 copper>Q235Csteel ?Q235A steel?45# steel.Current density has little effect on medium polarization.The interface voltage increases with the current density increasing.As the water content increases,the interfacial voltage increases and reaches to the maximum at 40% water content.Then it decreases and tends to be stable when the water content is larger than 50%.When foreign bodies such as carbon,water hole,copper added into the kaolin homogeneous body,the polarization rate of the mixture becomes much greater after subtracting the interface polarization voltage between the rock soil and the power supply electrode from the volume voltage.This method is of practical value for the improvement of the sensitivity of BEAM.